1. Field of the Invention
The present invention relates generally to the measurement of the radar cross section of an aircraft, ship or other military device for which it is required that the radar cross section be measured. In particular, the present invention relates to multistatic radar signature apparatus which measures radar cross section utilizing a sensor array of photonic receivers.
2. Description of the Prior Art
The bistatic radar detection of threat targets plays an important role in modern electronic warfare. Many weapon systems use bistatic radar signatures for target detection and tracking, end game weapon fusing, and target identification. Monostatic signatures are generally not acceptable for bistatic radar engagement scenarios due to variable radar-to-target illumination and target-to-receiver geometrics as well as the geometry of the target. Accordingly, bistatic radar cross section (RCS) measurements are required for an accurate analysis of almost all radar-to-target detection scenarios-whether the scenario is for surveillance or for tactical semi-active missile homing applications.
Prior art bistatic radar systems are generally characterized by the placement of the radar transmitter relative to the radar receiver in contrast to monostatic radar systems which collocate the transmitter and receiver. Bistatic radar cross section (RCS) measurements are generally made by physically moving the radar receiver with respect to the transmitter to cover the range of bistatic angles required for an accurate RCS measurement. This is also a requirement of two and three dimensional bistatic high-resolution RCS imaging apparatus which incorporate synthetic aperture radar or inverse synthetic aperture radar techniques.
Physically moving the receiver with respect to the radar transmitter to cover each bistatic angle for an RCS measurement is a distinct disadvantage of bistatic RCS measurement apparatus and methods because it requires data to be collected serially which slows the RCS measurement process and adds to the cost of making these measurements. This is true whether the receiver or sensors are moved by hand or electro-mechanically moved. Electro-mechanical RCS measurement systems are also susceptible to mechanical displacement errors of the receiver or sensors which renders the measurement data inaccurate as well as the resulting calculated RCS.
Prior art bistatic RCS measurement apparatus include standard RF/transmission lines to couple the radar receiver to a data acquisition and processing system which is normally located at a considerable distance from the receiver. These transmission lines are not advantages due to limitations of the lines imposed by attenuation and dispersion of the microwave signals transmitted through the lines.